What is the source of the RDU average rainfall as 39 inches...My google search found the following site (average from 1961-1990) that indicates an average closer to 44 inches... which would make our rainfall deficit and drought more severe. See http://www.ocs.orst.edu/pub/maps/Precipitation/Total/States/NC/nc.gif. Any clarification?
Posted December 1, 2007
MIKE MOSS SAYS: Doug, The map you cited is based on the 1961-1990 climate normals, which has been superseded by 1971-2000 values for some time now. For RDU, the normal annual rainfall based on the earlier period was 41.4 inches, while the current normal, based on the later 30-year period, is 43.1 inches.
I don't think that's the source of confusion here, though. Instead, I'm guessing the 39-inch value you noted is probably the normal "year-to-date" rainfall as of late November (I'm answering this on 1 Dec and the normal YTD is just up to 40.0 inches today and would have been around 39 a week ago) . The YTD value refers to how much rain would fall from January 1st until the current date, and will be less than the normal annual rainfall until we reach December 31st.